1. Technical Field
The present invention relates to an optical touch system.
2. Related Art
In optical touch systems, image sensors capture pictures having object images. The touch systems then analyze the positions of the object images of pictures, and calculate coordinates of the objects by the positions of the object images and some geometric dimensions of the touch systems.
U.S. Pat. No. 4,782,328 discloses a touch screen system comprising two sensors and a processor coupled with the two sensors. The sensors are used to capture images of an object on a touch screen. The processor analyzes the images, determines sensing paths respectively connecting the object and the two sensors, and calculates the coordinates of the object by the sensing paths.
Multi-touch systems allow users to simultaneously use at least one finger to interact with displayed content. With the multi-touch systems, users can move at least one finger on touch screens to generate corresponding gesture commands to control the displayed content. For example, moving a finger can scroll up or down lists or tables. Thus, the operation of moving a finger is called a scroll gesture. Pinching or reverse pinching can zoom out or in displayed content. Rotating gestures (i.e., moving an index finger around a thumb) can rotate an image.
Multi-touch applications can adopt an event driven model as their basic conceptual designs. After a computing system captures a touch event, a registered event handler is called to implement a desired functionality.
In optical multi-touch systems, when two fingers are applied, a picture generated by an image sensor will have two finger images. A corresponding gesture can be determined by analyzing pictures generated at multiple time points. When two fingers are too close to each other, a generated picture may show one image. Under such a circumstance, the touch system may incorrectly determine that the operation is performed by a single finger and calculate coordinates, resulting in incorrect coordinates or an incorrectly determined gesture.